Fatigue accelerated tests

Loading frequency and moderate variation of temperature have little effect upon the number of cycles to fracture in dry fatigue. These factors are more important in CF. The effect of frequency is significant because flie corrosion effect is time dependent, and the temperature is known to be an important factor in connection with corrosion. These two factors are mentioned at the same time because they both represent possible ways of accelerating CF tests. Reliable test results can, however, be obtained only if the fatigue acceleration factors are quantitatively known. 

Artificial aging -to- fi-sh n. The accelerated testing of plastics to determine their changes in properties such as dimensional stability, water resistance, resistance to chemicals and solvents, hght stabihty, and fatigue resistance. 

In equation 5, nj is the number of cycles within a block applied at stress level aj and Nj is the total number of cycles to failure at that stress level (obtained from the a-N curve). If validated for a particular material, equation 5 can be used for any arbitrary loading condition. In this way, the fatigue data generated in the laboratory is referred to as an accelerated test and equation 5 is used much in the same way that time-temperature superposition is used to predict the viscoelastic deformation of a material. Note, however, that any predictive methodology like that presented in equation 5 must be validated before it is employed for lifetime estimates. In the case of Minor s law, the sequence of the loading history should have no effect on the total lifetime. That is, if one specimen is loaded for a selected portion of its life at stress level stress level ct2 followed by CTi. 

Rdiability of semiconductor devices is determined by two considerations. The first one is early failures, usually caused by fluctuations in production, and the second one is fatigue, related to package design. Accelerated tests are necessa to detect those failures earlier. Many test methods have been proposed for development and assurance on the manufacturer s side and for incoming inspection on the user s... 

A less common use of accelerated tests is to estimate remaining lifetime. Heat ageing of two compounds and applying the time temperature superposition principle and models based on Miner s rule of cumulative material damage is described by Gillen and Cehna (41). However, Sun and co-workers (50) found that Miner s rule did not apply for fatigue of black filled NR and SBR. 

Miyano and Nakada proposed an accelerated method for the prediction of long-term creep and fatigue strength of FRP laminates on the basis of relatively few constant strain rate and fatigue loading tests. The following description of the methodology was first published in [1023]. This method is based on four assumptions ... 

Fig. 10 (a) The parameters of a sinusoidal fatigue cycle the strain amplitude, a, the strain range, s, the mean strain, the maximum strain, e ,ax and the minimum strain, Emin- (b) Temperature cycle responsible for TMF of soldered interconnections in service environments or during accelerated testing. 

Fatigue life corresponds to different accelerated tests performed on PBGA packages and FCOB with and without underfill. Strain and energy refer only to creep conponents, and are evaluated using FEA. 

Finally, the previous sections have discussed the methodology used to perform finite element prediction of the fatigue life of Sn-Ag-Cu solder joints in an accelerated test environment. The determination of the acceleration factor between accelerated test and product environments is an equally important component of the accelerated testing philosophy. For traditional high-lead solder interconnects, this has been performed with the Norris-Landzberg equation. 

Service lifetime prediction of polymers and/or polymer based materials may be undertaken from different types of tests, such as creep behavior tests (linear and non-linear creep, physical aging, time-dependent plasticity), fatigue behavior tests (stress transfer and normalized life prediction models, empirical fatigue theories, fracture mechanics theory and strength degradation) and standard accelerated aging tests (chemical resistance, thermal stability, liquid absorption) [32]. 

Kim GH, Lu H. Accelerated fatigue life testing of polycarbonate at low frequency under isothermal condition. Polym Test 2008 27(1) 114—21. 

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